Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of a molded article that can be formed, for example, from polyethylene terephthalate (PET) material is a preform that is capable of being subsequently blown into a beverage container, such as, a bottle and the like.
A typical molding system includes an injection unit, a clamp assembly and an injection mold. The injection unit can be, for example, of a reciprocating screw type or of a two-stage type. The clamp assembly includes, inter alia, a frame, a movable platen, a fixed platen and an actuator for moving the movable platen and to apply tonnage to the injection mold arranged between the platens. The injection mold includes, inter alia, a cold half and a hot half with one of more mold insert stacks disposed therein. Each mold insert stack typically includes a core insert and a cavity insert that cooperate, in use, to define a molding cavity. However, each mold insert stack can be associated with a number of additional components such as, for example, a split mold insert pair (sometimes referred to as neck rings), a gate insert, a retainer, or a support member. The hot half is usually associated with one or more cavities (and, hence, also sometimes referred to by those of skill in the art as a “cavity half”), while the cold half is usually associated with one or more cores (and, hence, also sometimes referred to by those of skill in the art as a “core half”). The hot half can also be associated with a melt distribution system (also referred to sometimes by those of skill in the art as a “hot runner”) for melt distribution. The injection mold can be associated with a number of additional components, such as slides for positioning of the split mold insert pair, ejector structures, wear pads, etc.
As an illustration, injection molding of PET material involves heating the PET material (ex. PET pellets, PEN powder, PLA, etc.) to a homogeneous molten state and injecting, under pressure, the so-melted PET material into the one or more molding cavities to form preforms. The cavity plate and the core plate are urged together and are held together by clamp force, the clamp force being sufficient enough to keep the cavity and the core pieces together against the pressure of the injected PET material. The molding cavity has a shape that substantially corresponds to a final cold-state shape of the molded article to be molded. The so-injected PET material is then cooled to a temperature sufficient to enable ejection of the so-formed molded article from the mold. When cooled, the molded article shrinks inside of the molding cavity and, as such, when the cavity and core plates are urged apart, the molded article tends to remain associated with the core. Accordingly, by urging the core plate away from the cavity plate, the molded article can be demolded, i.e. ejected from the core piece. Ejection structures are known to assist in removing the molded articles from the core halves. Examples of the ejection structures include stripper plates, ejector pins, etc.
One common example of a molded article that can be formed is a preform of the type that is capable of being subsequently blown into a beverage container, such as, a bottle and the like.